1. Field of the Invention
The present invention relates to container transport systems of the type in which containers are stored on leg-mounted pallet frames and the loaded pallet frames are moved by use of trailers having their beds adapted to be lowered to a level to be backed beneath a selected pallet frame and then raised to lift the legs of the pallet frame out of ground contact. More particularly, the invention provides improvements in both the trailer and pallet frame components of such a system, and the manner in which they interact during maneuvering of the trailer to back in beneath a pallet frame.
2. Description of the Prior Art
To elaborate, as discussed in U.S. Pat. No. 3,948,403 it is advantageous in loading and unloading a container ship to handle a group of standardized containers as a single load unit carried in a transportable pallet frame which is adapted to be raised out of ground contact by a complementing trailer after it is driven beneath the pallet frame. In the commercial embodiment of the system disclosed in said patent, known as the "Luf System", and marketed by Salen & Wicander Terminal System AB, Gothenburg, Sweden, the pallet frame is generally H-shaped in plan view with the two legs of the H comprising opposed side channels with which the longitudinal side rails of a special low-chassis semi-trailer interfit as the trailer is backed beneath the load frame by a suitable towing vehicle. The trailer has a relatively large number of vertically adjustably support wheels at the rear arranged in two parallel rows adjustable in height to raise the trailer chassis and thereby raise the pallet frame from ground contact.
In the Luf System there is very little tolerance between the side rails of the trailer and the side channels of the pallet frame with which they must interfit, and hence the driver of the towing vehicle has difficulty in backing the trailer into proper position. As a result the pallet frame transporting operation is made slower than it should be and lateral scuffing of the tractor tires on the road surface is commonly experienced while rearwardly maneuvering the trailer beneath the pallet frames.